Net Income Per Limited Partner Unit - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions								3 Months Ended		9 Months Ended
	Nov. 12, 2020	Aug. 13, 2020	May 14, 2020	Feb. 13, 2020	Aug. 14, 2019	May 15, 2019	Feb. 14, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Partner distributions declared	$ 37,600	$ 37,600	$ 37,600	$ 37,600	$ 34,400	$ 33,000	$ 31,600	$ 37,600	$ 35,900	$ 112,800	$ 103,100
Net income attributable to the Partnership in excess of distributions								7,700	9,800	14,800	17,100
Net income attributable to the Partnership								$ 45,300	$ 45,700	$ 127,600	$ 120,200
Weighted average units outstanding:
Basic and Diluted (in shares)								104.8	104.8	104.8	104.8
Incentive distribution rights currently held by the General Partner
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Partner distributions declared	1,200	1,200	1,200	1,200	400	200	0	$ 1,200	$ 700	$ 3,600	$ 1,300
Net income attributable to the Partnership in excess of distributions								0	0	0	0
Net income attributable to the Partnership								1,200	700	3,600	1,300
Limited partners' distribution declared on common units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Partner distributions declared	18,200	18,200	18,200	18,200	17,000	16,400	15,800	18,200	17,600	54,600	50,900
Net income attributable to the Partnership in excess of distributions								3,800	4,900	7,400	8,600
Net income attributable to the Partnership								$ 22,000	$ 22,500	$ 62,000	$ 59,500
Weighted average units outstanding:
Basic and Diluted (in shares)								52.4	52.4	52.4	52.4
Net income per limited partner unit (in dollars):
Basic and Diluted (in dollars per share)								$ 0.42	$ 0.43	$ 1.19	$ 1.13
Limited partners' distribution declared on subordinated units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Partner distributions declared	$ 18,200	$ 18,200	$ 18,200	$ 18,200	$ 17,000	$ 16,400	$ 15,800	$ 18,200	$ 17,600	$ 54,600	$ 50,900
Net income attributable to the Partnership in excess of distributions								3,900	4,900	7,400	8,500
Net income attributable to the Partnership								$ 22,100	$ 22,500	$ 62,000	$ 59,400
Weighted average units outstanding:
Basic and Diluted (in shares)								52.4	52.4	52.4	52.4
Net income per limited partner unit (in dollars):
Basic and Diluted (in dollars per share)								$ 0.42	$ 0.43	$ 1.19	$ 1.13